Heat recovery gas turbine in combined brayton cycle power generation

Abstract

A combined Brayton cycle power plant ( 5 ). A combustion gas turbine engine ( 21 ) in the power plant uses a first Brayton cycle ( 20 ), and produces waste heat in an exhaust combustion gas ( 36 ). A heat exchanger ( 58 ) transfers the waste heat to a compressed working airflow ( 56 ) for a second Brayton cycle ( 50 ) in a heat recovery gas turbine engine ( 51 ). The heat transfer lowers the temperature of the combustion exhaust gas ( 36 ) to within an operating range of a conventional selective catalytic reduction unit ( 80 ), for efficient reduction of nitrogen oxide emissions to meet environmental regulations.

1 . A power generator comprising: 
 a first Brayton cycle engine comprising a first airflow, a fuel input, and a fuel combustion in the first airflow producing combustion gas exhaust, the first Brayton cycle engine producing a first shaft power; and    a second Brayton cycle engine comprising a second airflow and a heat exchanger that transfers heat from the first combustion gas exhaust to the second airflow, the second Brayton cycle engine producing a second shaft power.    
     
     
         2 . The power generator of  claim 1 , further comprising a selective catalytic reduction unit associated with the combustion gas exhaust downstream of the heat exchanger.  
     
     
         3 . The power generator of  claim 1 , wherein the second airflow comprises an inlet portion, a compressed portion that passes through the heat exchanger, a heated compressed portion that leaves the heat exchanger, a portion that expands in a turbine section, and an exhaust air portion.  
     
     
         4 . The power generator of  claim 3 , wherein the second airflow inlet portion comprises an inlet pressure, and the compressed portion has a pressure 4 to 6 times greater than the inlet pressure.  
     
     
         5 . The power generator of  claim 4  wherein the second Brayton cycle engine comprises a combustion gas turbine engine of a type comprising a combustion chamber and a plurality of compressor stages and modified by replacing the combustion chamber with the heat exchanger and eliminating at least one of the compressor stages and at least one of the turbine section stages.  
     
     
         6 . The power generator of  claim 1 , further comprising an electrical generator, wherein the first and second shaft powers are applied to a common electrical generator.  
     
     
         7 . A method for increasing efficiency and reducing nitrogen oxide emissions in a combustion gas turbine power generator of a type that produces a combustion gas exhaust, the method comprising: 
 ducting the combustion gas exhaust to a heat recovery gas turbine engine that compresses a working airflow, then transfers heat energy from the combustion gas exhaust to the working airflow, then expands the working airflow in a turbine section to produce a shaft power; and    passing the combustion gas exhaust through a selective catalytic reduction process downstream of the heat recovery gas turbine engine to reduce a nitrogen oxide emission in the combustion gas exhaust.    
     
     
         8 . The method of  claim 7 , further comprising: 
 making the heat recovery gas turbine engine from a combustion gas turbine engine of a type comprising a combustion chamber and a plurality of compressor stages by replacing the combustion chamber with a heat exchanger and removing at least one of the compressor stages and at least one of the turbine section stages; and    ducting the combustion gas exhaust to the heat exchanger to transfer heat to the working airflow of the heat recovery gas turbine engine.    
     
     
         9 . A power generator comprising: 
 a combustion gas turbine engine that draws a first airflow, compresses it, mixes it with fuel, then combusts the first airflow and fuel mixture producing a combustion gas flow, then expands the combustion gas flow in a turbine section to produce a first shaft power, then exhausts the combustion gas flow;    a heat recovery gas turbine engine that draws a second airflow, compresses it, then heats it in a heat exchanger by transferring heat from the exhausted combustion gas flow to the compressed second airflow, then expands the compressed heated second airflow in a turbine section to produce a second shaft power; and    a selective catalytic reduction unit that receives the exhausted combustion gas flow downstream of the heat exchanger.    
     
     
         10 . The power generator of  claim 9 , wherein the heat recovery gas turbine engine comprises a compressor section with a compression ratio of between 4 and 6.  
     
     
         11 . The power generator of  claim 10 , wherein the heat recovery gas turbine engine is designed by modifying a combustion gas turbine engine design of a type comprising a combustion chamber and a plurality of compressor stages, the modification comprising replacing the combustion chamber with the heat exchanger, and eliminating at least one of the compressor stages and at least one of the turbine section stages.  
     
     
         12 . The power generator of  claim 9 , further comprising an electrical generator, wherein the first and second shaft powers are applied to a common electrical generator.